# std::experimental::nullopt_t

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< cpp‎ | experimental‎ | optional

Defined in header `<experimental/optional>` |  |
struct nullopt_t; |  | (library fundamentals TS)

`std::experimental::nullopt_t` is an empty class type used to indicate `optional` type with uninitialized state. In particular, std::experimental::optional has a constructor with `nullopt_t` as a single argument, which creates an optional that does not contain a value.

`std::experimental::nullopt_t` must be a LiteralType and cannot have a default constructor.

It must have a `constexpr` constructor that takes some implementation-defined literal type.

### Notes

`nullopt_t` is not DefaultConstructible to support both op = {}; and op = nullopt; as the syntax for disengaging an optional object.

A possible implementation of this class is

    struct nullopt_t
    {
        constexpr nullopt_t(int) {}
    };

### See also

nullopt (C++17) | an object of type `nullopt_t` (constant)

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